The effects of particle properties, especially the surface roughness and particle type, on the gravity discharge rate and flow behavior of fine dry powders from a conical hopper are studied in detail. The van der Waals force is considered to dominate the discharge of small particles, while the empty annulus effect dominates the discharge of large particles. To predict the van der Waals force between two rough spherical particles, a model based on Rumpf theory is adopted. The effect of surface roughness can be reflected by Bond number Bo_g which is correlated with discharge rate. By modifying the powder bed porosity and Beverloo constant, the discharge rates of fine dry powders can be well predicted by an empirical correlation. Finally, not only the ratio of hopper outlet size to particle size D₀/d_p but also the Bond number Bo_g is found to be an important indicator to determine the powder flowability. © 2017 American Institute of Chemical Engineers AIChE J, 2017

中文翻译：

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从锥形料斗中引出细微干粉的重力引力

详细研究了颗粒性质，特别是表面粗糙度和颗粒类型对锥形料斗中细干粉的重力排放速率和流动行为的影响。范德华力被认为是小颗粒排放的主导因素，而空环空效应则是大颗粒排放的主导因素。为了预测两个粗糙球形颗粒之间的范德华力，采用了基于Rumpf理论的模型。表面粗糙度的影响可以通过与放电速率相关的结合数Bo _g来反映。通过改变粉末床的孔隙率和Beverloo常数，可以通过经验相关性很好地预测干粉的排放速率。最后，不仅是料斗出口尺寸与粒径D _0之比/ d _p以及键数Bo _g被发现是确定粉末流动性的重要指标。©2017美国化学工程师学会AIChE J，2017